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From: "Gumpula, Suresh" <Suresh.Gumpula@netapp.com>
To: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>
Subject: malloc(9)  and its alignment
Thread-Topic: malloc(9)  and its alignment
Thread-Index: Ac8nlkbcQYqIQNi5TDadKkROsoUT6Q==
Date: Wed, 12 Feb 2014 02:02:01 +0000
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Hi,
It appears  the malloc(9) returns 8 byte aligned ( UMA_ALIGN_PTR) pointers,=
 but in bus_dmamem_alloc  we might end up checking for greater alignment
if we take malloc(9) path instead contig_malloc.
Can someone please confirm if malloc(9) returns different alignment pointer=
s ?

bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
                 bus_dmamap_t *mapp)
{
        /*
         * XXX:
         * (dmat->alignment < dmat->maxsize) is just a quick hack; the exac=
t
         * alignment guarantees of malloc need to be nailed down, and the
         * code below should be rewritten to take that into account.
         *
         * In the meantime, we'll warn the user if malloc gets it wrong.
         */
        if ((dmat->maxsize <=3D PAGE_SIZE) &&
           (dmat->alignment < dmat->maxsize) &&
            dmat->lowaddr >=3D ptoa((vm_paddr_t)Maxmem)) {
                *vaddr =3D malloc(dmat->maxsize, M_DEVBUF, mflags);
        } else {

                *vaddr =3D contigmalloc(dmat->maxsize, M_DEVBUF, mflags,
                    0ul, dmat->lowaddr, dmat->alignment? dmat->alignment : =
1ul,
                    dmat->boundary);
       }=20
        if (vtophys(*vaddr) & (dmat->alignment - 1)) {
                NETAPP_MUTED_PRINTF("bus_dmamem_alloc failed to align memor=
y properly.\n");

Regards,
Suresh